1. Field of the Invention
This invention relates to an apparatus and process for heating, ventilating and humidifying residential and commercial enclosures. This invention utilizes the aqueous condensate from products of combustion in the secondary integral heat exchanger of a high efficiency furnace to humidify the primary heated air passing from the furnace to the conditioned space.
2. Description of Related Art
Heat recovery from hot flue gases for a variety of purposes is known: U.S. Pat. No. 4,138,062 teaches preheating outside air for introduction to the return plenum by indirect thermal exchange with flue gas; U.S. Pat. No. 4,241,874 teaches preheating outside air for combustion by indirect thermal exchange with flue gases; U.S. Pat. No. 4,028,817 teaches preheating outside air for introduction to a dryer by indirect thermal exchange with flue gases of a gas dryer; U.S. Pat. No. 4,485,746 and 4,318,367 teach generation of hot water by indirect thermal exchange with flue gases; and U.S. Pat. No. 4,175,518 teaches preheating incoming cold water to a hot water heater by indirect thermal exchange with flue gases.
Humidification of circulating air in the plenum or warm air duct of a furnace is known: U.S. Pat. No. 3,592,182 teaches evaporation from a sponge in an air-foil shaped water reservoir, supplied by an external water source, in a horizontal warm air duct; and U.S. Pat. Nos. 4,922,890; 4,987,881; 3,612,033; 3,491,746; 3,472,496; 3,033,193; and 3,021,831 teach supply of water from household plumbing to a porous evaporator in a furnace plenum or warm air duct, noting problems caused by minerals in the water. Generation of steam from water supplied from an external source by thermal transfer with hot flue gases and passage of the generated steam into the warm air duct for humidification is taught by U.S. Pat. No. 3,443,559 and 4,257,389, the 4,257,389 patent noting the problems created by minerals in water from a standard water line and suggesting softening or filtration. U.S. Pat. No. 4,410,136 teaches an annular passage surrounding a furnace flue into the upper portion of which return air is introduced and household water sprayed onto the flue causing evaporation of the water, thereby humidifying the air, with condensation from the flue being drained from the system. U.S. Pat. No. 4,706,884 teaches a flue gas heat exchanger in the return duct of a hot air furnace which collects condensation from the flue gases and its use for humidification in the return air duct or in the warm air duct. The U.S. Pat. No. 4,706,884 points out a serious problem with the disclosed system being that the return duct is under a negative pressure with respect to the flue gas heat exchanger, and thus, any leaks would pass from the flue gas heat exchanger into the return air, which would be intolerable from a practical safety standpoint. Retrofit of the unit disclosed by the U.S. Pat. No. 4,706,884 may also affect the combustion process of the furnace design.
In view of increasing fuel costs in recent years, high efficiency, or condensing, furnaces have gained widespread use due to their efficiency of about 90 percent plus. The high efficiency furnace has a very efficient thermal exchanger downstream of the combustion burners providing highly efficient indirect thermal exchange between the gases formed by combustion and the air being heated. Since water is a product of combustion, the highly efficient thermal exchange results in sufficient cooling of the gases formed by combustion to form considerable aqueous condensation. Conventionally, the condensed water is drained from the furnace and discharged through a household drain.